This invention relates to an anti-lock brake control device for a motor vehicle.
Traditionally, when a braking system is switched in an anti-lock brake control mode, an anti-lock brake controller conducts a select-low control subroutine with regard to a rear wheel in order to secure stability of the vehicle by reducing or eliminating wheel lock. During a select-low control subroutine, the hydraulic pressure in the rear wheel is reduced or held, even if the rear wheel does not indicate a locking situation or a signal that the wheel is beginning to lock. A significant amount of brake fluid is xe2x80x9cconsumedxe2x80x9d or passed through the system during an anti-lock braking procedure, as the pressure in the system is increased by opening an inlet valve to supply fluid to the system while an outlet valve is closed to increase the pressure; both inlet and outlet valves are closed to maintain pressure; and the outlet valve is opened with the inlet valve closed, to decrease pressure. Because of this, an anti-lock braking system requires a larger storage capacity of braking fluid than in a standard system, as well as a larger motor and/or pump to cycle the fluid. Further, because the select-low routine reduces or holds the pressure in the rear wheels even when the rear wheel does not show a tendency to be locked, this reduces the amount of braking force which could otherwise be achieved if the pressure were not held constant or reduced on the rear wheels in such situations.
Still further, even if the anti-lock brake control device conducts a braking force distribution control routine, after the rear wheel control is switched to an anti-lock brake control mode, the brake fluid consumption increases by frequently repeating the pressure increase and decrease. In order to refill the increased fluid, the system requires a larger motor or pump.
The present invention is directed toward more appropriate application of anti-lock braking control while also reducing the amount of brake fluid consumption that is currently experienced by anti-lock braking control systems. Systems and methods of accomplishing the foregoing are disclosed. An anti-lock brake control system typically includes a hydraulic unit having a main hydraulic circuit connecting a master cylinder and a wheel cylinder via an inlet valve, and an auxiliary hydraulic circuit connecting a wheel cylinder and an auxiliary reservoir via an outlet valve. A wheel speed sensor is provided for each wheel for determining wheel speed thereof. An electronic control device controls the hydraulic unit.
In one aspect of the present invention, if a deceleration of a rear wheel is larger than a deceleration of a front wheel, the rear wheel is controlled individually, and if deceleration of the rear wheel is not larger than a deceleration of the front wheel, the rear wheel is controlled on a select-low basis.
According to another aspect of the present invention, if anti-lock brake control is provided upon conducting braking force distribution control, a rear wheel is controlled individually, and if anti-lock control is provided while not under braking force distribution control, a rear wheel is controlled on a select-low basis. The individual control may be a continuance of the braking force distribution control.
Another aspect of the present invention is controlling of the braking such that the rear wheels are controlled on a select-low basis when it has been determined that one or more wheels are contacting a low xcexc road surface or if a large decompression has occurred.
Still further, a restraint means may be provided to prohibit a pressure increase in a wheel cylinder when an estimated wheel deceleration is larger than a predetermined deceleration value and a wheel slip ratio is larger than a predetermined wheel slip ratio value. The restraint means may prohibit a pressure increase in a wheel cylinder on a non-driving wheel for a duration that is longer than a duration during which a pressure increase in a wheel cylinder on a driving wheel is prohibited. The restraint means may extend its duration of operation based on a number of pressure increase cycles accomplished by the anti-lock brake control procedure. The restrain means may extend its duration of operation based on an amount of wheel speed. The restraint means may be disabled when a number of pressure increase cycles accomplished by the anti-lock braking control subroutine exceeds a predetermined value. The restraint means may be disabled when a wheel acceleration exceeds a predetermined value.
A method of controlling braking according to one aspect of the present invention, includes estimating front and rear wheel deceleration values based on wheel speed calculations; comparing the estimated rear wheel deceleration value with the estimated front wheel deceleration value to determine which value is greater; controlling braking of the rear wheels independently if the estimated rear wheel deceleration is larger than the estimated front wheel deceleration; and controlling braking of the rear wheels by select-low control if the estimated rear wheel deceleration is not larger than the estimated front wheel deceleration.
In another aspect of the invention, a determination of whether to apply braking force distribution control is made upon the initiation of braking. Braking of the rear wheels are controlled independently while controlling braking of the front wheels under anti-lock braking control when braking force distribution control has been initiated and it becomes necessary to apply anti-lock braking control to the front wheels. The independent control may be a continuance of the braking force distribution control. Braking of the rear wheels are controlled under select-low braking control while controlling braking of the front wheels under anti-lock braking control when braking force distribution control has not been initiated and it becomes necessary to apply anti-lock braking control to the front wheels.
Braking control with regard to low xcexc road surfaces may include estimating front and rear wheel deceleration values based on wheel speed calculations; determining that one or more wheels are on a low xcexc road surface if one or more estimated deceleration values exceeds a predetermined value; and controlling braking of the rear wheels under select-low control when it has been determined that one or more wheels are on a low xcexc road surface.
According to another aspect of the present invention, a method of controlling braking includes estimating front and rear wheel deceleration values based on wheel speed calculations; estimating front and rear wheel slip ratios, for example by subtracting vehicle speed from wheel speed and dividing the difference by vehicle speed; and prohibiting hydraulic pressure increase to rear wheel cylinders of the rear wheels when an estimated wheel deceleration is larger than a predetermined deceleration value and a wheel slip ratio is larger than a predetermined wheel slip ratio value. The prohibition may include prohibiting a pressure increase in a wheel cylinder on a non-driving wheel for a duration that is longer than a duration during which a pressure increase in a wheel cylinder on a driving wheel is prohibited. Further, the prohibition may be extended in duration when a number of pressure increase cycles accomplished by an anti-lock brake control procedure exceeds a predetermined number. A duration of prohibiting may be determined based upon wheel speed. Prohibition may be discontinued when a number of pressure increase cycles accomplished by anti-lock braking control exceeds a predetermined value. Prohibition may be disabled when a wheel acceleration exceeds a predetermined value.
These and other objects, advantages, and features of the invention will become apparent to those persons skilled in the art upon reading the details of the invention as more fully described below.